(1) Field of the Invention
This invention relates to a column for high-pressure liquid chromatography, wherein the column includes a tube which can be filled with a sorbent packing and an inlet device and outlet device at the ends of the tube. The invention further relates to a process for filling such a tube with sorbent packing.
(2) Prior Art and Technical Considerations
In order to obtain columns having good resolving power, a very fine particulate sorbent material is used. For example silica gel having a particle size of about 5 to 50 .mu.m, is introduced into the column as uniformly as possible in a tightly packed state. Filling the column is usually effected by closing the column at one end with an outlet device containing a filter element and filling the column with a suspension of the sorbent material via a filling device mounted at the other end, the sorbent material being retained by the filter element, while the carrier liquid passes through substantially unhindered. Filling is carried out under a predetermined high pressure of up to a few hundred bar, for example up to 500 to 700 bar, whereby very tight packing is achieved.
However, it is not possible to maintain the pressure on the packing when the filling device is uncoupled upon completion of the filling process. It has been found that as a result of this depressurization, there is a spring back of the packing, and the sorbent gushes out to some extent from the column tube. The solid stress built up in the filling operation is therefore reduced and, when the column is operated under a restored high pressure, collapse of the packing can result.
Numerous attempts have already been made to improve this situation. Thus, chromatography columns in which the sorbent packing is stabilized by means of a pressed-on plunger are described, for example, in German Offenlegungsschrift No. 30 21 366 and European published application No. 0,040,663. A column which has a flexible external wall whereby stabilization of the packing is achieved by radial compression of the separating column is described in German Offenlegungsschrift No. 30 00 475.
All these solutions require a considerable technical outlay. Moreover these solutions cannot ensure that a packing, once depressurized, can be brought back, by means of external pressure, into a state corresponding to the original packing density.
It is therefore necessary to provide a practical means for maintaining the solid stress built up after the column was filled and thus obtain a stable packing having long-term, separation avoiding properties.